This invention relates to a method for adjusting a governor actuator in a traction control system, and more particularly to a method for adjusting a governor actuator for actuation and control of a governor link adjusting an output of an engine of a vehicle in a traction control system which is adapted to adjust drive power of drive wheels of the vehicle to prevent waste of power of the engine due to slipping of the drive wheels at the time of start or quick acceleration of the vehicle and ensure positive start and acceleration of the engine.
In an automobile industry, an anti skid brake control (hereinafter also referred to as "ABS") system has been developed which is adapted to adjust brake force to prevent locking of brake wheels during braking of a vehicle. Also, a traction control (hereinafter also referred to as "TRC") system has been conventionally proposed which is adapted to adjust driving force of drive wheels of the vehicle to minimize power loss of an engine during slipping of the drive wheels and more effectively transmit driving force of the drive wheels to a road surface to promote propulsion of the vehicle.
Such an ABS/TRC system may be constructed, for example, in such a manner as shown in FIG. 2. More particularly, the ABS/TRC system generally includes a pair of wheel speed sensors 3 and 4 for detecting a wheel speed of a pair of front wheels 1 and 2 each acting as a non-drive wheel; a modulator 5 for adjusting a brake pressure of the front wheels 1 and 2; a brake chamber 6 which acts to permit the front wheels 1 and 2 to generate brake force; wheel speed sensors 9 and 10 for detecting a wheel speed of a pair of rear wheels 7 and 8 each acting as a drive wheel; modulators 11 and 12 arranged for adjusting a brake pressure of the rear wheels 7 and 8; brake chambers 13 and 14 acting to permit the rear wheels 7 and 8 to generate brake force; a dual brake valve 16 of which operation is controlled by a brake pedal 15; traction solenoid valves (hereinafter also referred to as "TRC" valves) each comprising a solenoid valve and kept open at the time of traction control (TRC) to feed compressed air in an air tank 17 to the modules 11 and 12 for the rear wheels 7 and 8; a governor actuator 21 for actuating a governor link 20 adapted to vary and set a lower limit value of an engine speed of an engine E; and an ABS/TRC control unit (Hereinafter also referred to as "ABS/TRC ECU") 22 for controlling the modules 5, 11 and 12, traction solenoid valves 18 and 19, and governor actuator 21. In FIG. 2, reference numeral 23 designates an accelerator pedal.
Thus, the ABS/TRC system shown in FIG. 2 is constructed into a four-sensor and three- channel control systems wherein four such wheel speed sensors 3, 4, 9 and 10 are provided for the two front wheels and two rear wheels, respectively, and the single modulator 5 is arranged common to the front wheels 1 and 2 and each one modulator is provided for each of the rear wheels 7 and 8.
The ABS/TRC system of FIG. 2 constructed as described above is so operated that a wheel speed signal is fed from each of the wheel speed sensors 3, 4, 9 and 10 to the ABS/TRC ECU 22. Then, the ABS/TRC ECU 22 carries out operation based on the thus fed wheel speed signal during braking. As a result, when the ABS/TRC ECU 22 judges that the wheels tend to skid, it feeds a control signal to each of the modulators 5, 11 and 12 corresponding to the wheels tending to skid. This results in the modulators 5, 11 and 12 adjusting a brake pressure in the brake chambers 6, 13 and 14 to eliminate the tendency of skid of the wheels. Thus, the ABS/TRC ECU 22 carries out antiskid brake control to eliminate the tendency of wheel locking when the tendency of wheel locking tends to occur during braking.
Also, during an increase in propulsion of the vehicle at the time of start or quick acceleration of the vehicle, the ABS/TRC ECU 22 carries out operation depending on the wheel speed signal fed thereto from each of the wheel speed sensors 3, 4, 9 and 10. As a result, when the ABS/TRC ECU 22 judges that the rear wheels 7 and 8 each acting as a drive wheel tend to slip, it feeds a control signal to each of the modulators 11 and 12 and TRC valves 18 and 19 corresponding to the rear wheels 7 and 8 tending to slip, as well as to the governor actuator 21 for actuating the governor link 20.
The control signal thus fed causes the TRC valves 18 and 19 to be open, so that compressed air may be fed from the air tank 17 through the TRC valves 18 and 19, double check valves 24 and 25, and modulators 11 and 12 to the brake chambers 13 and 14, leading to braking of the rear wheels 7 and 8 that tend to slip. This results in the tendency of slipping of the rear wheels 7 and 8 being eliminated.
An example of TRC due to such braking of the drive wheels is shown in FIG. 3.
In FIG. 3, the TRC is kept non controlled at time T0, therefore, a brake pressure is not generated, so that braking of the rear wheels 7 and 8 does not occur. At time T1, when the ABS/TRC ECU 22 judges that a wheel speed of the rear wheels 7 and 8 on a low .mu. side relative to a vehicle speed exceeds a predetermined threshold to cause the rear wheels 7 and 8 on the low .mu. side to tend to slip, it feed the TRC valves 18 and 19 with a control signal. The control signal thus fed from the ABS/TRC ECU 22 to the TRC valves 18 and 19 causes the rear wheels 7 and 8 on the low .mu. side to be turned on, to thereby brake the rear wheels 7 and 8 that tend to slip. Thus, the TRC due to braking is started. For a predetermined of time after starting of the braking, a relatively long build pulse is out put to a holding solenoid valve (not shown) of each of the modulators 11 and 12 for the purpose of removal of hysteresis in a brake system to repeat on off operation of the holding solenoid valves. At time T2, a slow increase in brake pressure is started. A plurality of rates at which such a slow increase in brake pressure is carried out is set depending on the amount of slipping of the drive wheels or the magnitude of a road surface .mu.. When the tendency of slipping the wheels tends to reduce, the holding solenoid valve of each of the modulators 11 and 12 is turned on at time T3 and concurrently an exhaust solenoid valve (not shown) of each of the modulators 11 and 12 is turned off or kept turned on for a short period of time, so that the brake pressure is kept or reduced, resulting in a degree of recovering of the wheels being monitored. Start of the vehicle is carried out under such conditions. When the amount of slipping of the wheels is considerably reduced, the brake pressure is further decreased at time T4. When such a decrease in brake pressure causes the amount of slipping of the rear wheels 7 and 8 to be gradually increased again, a slow increase in brake pressure is started at time T5 in view of the tendency of slipping of the rear wheels 7 and 8, to thereby adjust the brake pressure. Then, depending on the tendency of slipping of the drive wheels, holding of the brake pressure or a decrease in brake pressure is carried out at time T6 in the same manner as that at time T3 described above. When the tendency of slipping of the rear wheels 7 and 8 is eliminated, the TRC valves 18 and 19 are turned off at time T8 to interrupt feed of air from the air tank 17. Concurrently, the modulators 11 and 12 are kept actuated to discharge a pressure remaining in a piping system. Then, the modulators 11 and 12 are turned off at time T9 after a predetermined time elapses, resulting in the TRC being terminated.
The above-described control signal output from the ABS/TRC ECU 22 also causes the governor actuators 21 to rotate to adjust the governor 20 of the engine E, so that the engine E is subject to control for speed reduction or deceleration. Such deceleration of the engine E causes rotational driving force of the rear wheels 7 and 8 to be restrained, resulting in the tendency of slipping of the rear wheels that tend to slip being eliminated. Also, the engine E is subject to control for deceleration at the time of TRC due to braking of the rear wheels 7 and 8 as well, so that a lower limit value of an engine speed of the engine E is adjusted or changed to a lower limit value thereof obtained at the time of somewhat increased TRC so as to prevent any engine trouble from occurring at the time of TRC due to braking of the rear wheels 7 and 8.
An example of TRC due to such deceleration of the engine is shown in FIG. 4.
In the TRC due to deceleration of the engine, when the rear wheels 7 and 8 tend to slip after start of the vehicle begins at time t0, the ABS/TRC ECU 22 detects the tendency of slipping of the wheels to feed the governor actuator 21 with a control signal at time t1. This results in deceleration of the engine starting at a low deceleration rate. However, when a revolving speed of a drive shaft that indicates an average speed between the rear wheels 7 and 8 exceeds an allowable level at time t2, deceleration of the engine E is carried out at a full deceleration rate. When the tendency of slipping of the wheels is decreased, deceleration of the engine E is gradually released at time t3. In other words, the engine is accelerated at a low acceleration rate. In this instance, the engine E is subject to quick acceleration depending on the amount of slipping of the wheels and a degree of deceleration of the drive shaft that indicates an average of deceleration between the rear wheels 7 and 8. When the tendency of slipping of only one of the rear wheels 7 and 8 is increased again under such conditions, corresponding one of the TRC valves 18 and 19 is turned on at time t4 to brake the one of the rear wheels that tends to slip and start deceleration of the engine. This causes the tendency of slipping of the one of the rear wheels 7 and 8 to be decreased. However, when this causes the tendency of slipping of the other of the rear wheels 7 and 8 to be concurrently reduced, there is a possibility that the engine causes any engine trouble. In order to avoid the problem, the engine E is subject to quick acceleration at time t5. When such quick acceleration of the engine E causes the tendency of slipping of the rear wheels to be increased again, the engine is subject to quick deceleration again at time t6. In this instance, the engine is subject to low deceleration depending on a degree of acceleration of the drive shaft indicating an average of acceleration between rear wheels 7 and 8 and the amount of slipping of the rear wheels. Then, when the wheel speed of each of the rear wheels 7 and 8 tends to reduce, the engine E is subject to slow acceleration at time t7. A degree of the slow acceleration is calculated on the basis of an internal integration value of a deceleration indication value and the internal integration value is calculated on the basis of behavior of the wheels and a deceleration indication value previously obtained. Thus, the TRC is carried out until the tendency of slipping of the rear wheels 7 and 8 is eliminated.
As described above, the ABS/TRC ECU 22 carries out the TRC due to braking of the drive wheels and the TRC due to deceleration of the engine so as to eliminate the tendency of slipping of the drive wheels or rear wheels 7 and 8 when they tend to slip. Also, the ABS/TRC ECU 22 is adapted to light a traction pilot lamp 26 during the TRC to inform a driver of the TRC when it is being carried out.
In the above-described conventional TRC due to control of the engine and braking of the drive wheels, the engine control in a normal state is carried out in a manner different from that at the time of TRC. Such change of the engine control is carried out by changing adjustment of the governor of the engine. For the change of adjustment of the governor, it is required to adjust the governor link 20 at the time of mounting of the ABS/TRC system on the vehicle or maintenance of the vehicle.
Adjustment of the governor link conventionally takes place in such a manner to connect a switch and a harness to the ABS/TRC ECU 22 and turn on the switch to externally input a signal to the ABS/TRC ECU 22, resulting in an operator executing adjustment of a governor link system while keeping a predetermined position servo signal fed from the ABS/TRC ECU 22 to the governor actuator 21.
Unfortunately, the above described conventional way of adjusting the governor link is disadvantageous in that the adjustment is highly deteriorated in workability and requires skill, resulting in being highly troublesome, because it is required to connect the switch and harness to the ABS/TRC ECU 22 every time when the adjustment takes places and it is required to carry out the adjustment while keeping the engine actuated. Also, the adjustment requires a specific switch, as well as a specific harness.